… and then one day, you wake up from the cloud of love drugs that you're brain's been swimming in for the last few months. Suddenly Mr/Ms Answer To Your Dreams isn't looking so hot. And what is that smell??? Following a rapid decline in interpersonal niceties and oxytocin-induced smiles, on goes the Patsy Cline collection, some tragic vids and a few sly grogs. Next stop: depression central, population you, you big loser.

Not surprisingly, there's more than a little chemistry involved in hiding under the doona for weeks at a time. And the fact that nobody knows exactly what causes depression hasn't stopped anyone from treating it.

Anti-depressants, like so many of science's big hits, were discovered by accident. A drug given to tuberculosis patients in the early 50's not only cured them of TB, it made them suspiciously happy. The drug was a monoamine oxidase (MAO) inhibitor. MAO breaks down noradrenaline and dopamine in the body. Depressed people usually have low levels of serotonin (another neurotransmitter) and noradrenaline, so MAO inhibiting drugs help by increasing these.

Of course it wasn't all smooth sailing in the early days: a few depressed patients on MAO inhibitors died after eating things like aged cheese. It turned out that the cheese contained lots of tyramine - an amino acid in food that's usually broken down by MAO in the gut, but is poisonous if it gets in whole. The drugs weren't taken off the market - but they came with a list of foods to avoid when taking them, and proceeded to sell like hot cakes. It seemed that nobody wanted to be depressed - least of all the pharmaceutical market. So the race was on to develop a pill that would let you eat the odd slab of vintage cheddar and feel better.

Doctors who didn't opt for shares in Prozac must be kicking themselves by now. The Western World's favourite aperitif can make most people who take it feel pretty fine. Instead of stopping the breakdown of serotonin (like MAO inhibitors), Prozac increases serotonin levels by stopping nerve cells from reabsorbing it once it's released. Acclaimed as a picker-upper that helps ward off anxiety, Prozac isn't completely without a downside.

For one thing, mixing Prozac with MAO inhibitors can lead to serotonin overload, causing the odd death. Less fatal, but just as newsworthy, Prozac-style drugs can also play havoc with libido and sexual performance. To top it off, not everyone feels great on Prozac - in some people it just flattens mood, making emotions feel less intense. Mind you, if you're spiralling ever deeper into a pit of despair, a little less intensity could be just the ticket.

If all this drug business sounds far too unnatural, try scoffing a tab of St John's Wort with your beer/coffee/fag. It contains hypericum, which works in much the same way as Prozac, but because it's a plant extract that's sold over the counter it's one drug that won't damage your tie-dyed reputation.